Add warning when the user doesn't pad the hydrological months properly

[albangossard]

Following #141 we have a way to pad the hydrological months in a flexible way to accommodate for specific measurement periods. However, if the user doesn't set the padding of the hydrological months properly with respect to the data, this will result in an error, cf this comment.
We should add a warning or an error to check that the data is in accordance with how the months are padded.